Data transmission device

ABSTRACT

In a device for data transmission having a central station and a plurality of subscribers, in addition to useful signal data phases, signaling data phases are provided for the downlink and uplink in a transmission frame ( 3 ). The signaling data phases for the downlink are divided into signaling data phases related to the central station and related to the protocol. The positions of these two signaling data phases are identified directly or indirectly by identifiers.

FIELD OF THE INVENTION

The present invention relates to a data transmission device on a commonmedium having a central station and a plurality of subscribers, which iscontrollable by transmitting data packets from the central station tothe subscribers (downlink) and from the subscribers to the centralstation (uplink).

BACKGROUND INFORMATION

German Patent Application No. 197 26 120 describes a device where thecentral station assumes the coordinating function for media access via aprotocol-oriented transmission frame referred to there as signalingperiods. This transmission frame contains, in addition to the usefulsignal data phases, signaling data phases for the uplink and thedownlink.

The method described in German Patent Application No. 197 26 120includes the step that the position of the downlink signaling isannounced in the previous downlink signaling. This method presents theproblem that a subscriber (terminal) that wishes to log into thecommunication process has no previous information regarding the positionof the downlink signaling (Broadcast Channel, BCH). Therefore, thisterminal must demodulate the transmission channel until it has found aBCH and has demodulated the information about the position of the nextBCH. Access to the transmission channel can therefore only take place inthe following transmission frame.

SUMMARY

In accordance with an example embodiment of the present invention,faster access to the transmission channel is made possible. By dividingthe downlink signaling data phase into signaling data phases related tothe central station and related to the protocol, these two signalingdata phases can be flexibly positioned at different points of thetransmission frame. This allows the available transmission capacity tobe fully utilized, in particular in the case where the DL-PDUs (DownlinkProtocol Data Units) are composed of elements having different lengths.If the position of the BCH were constant, it might not be possible tofill the entire period between the start of the transmission frame andthe protocol-related signaling data phase with useful data due to theflexible duration of the DL-PDUs. This would result in loss oftransmission capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a communication network having a central station andsubscribers connected through a common medium.

FIG. 2 shows the basic structure of a transmission frame according to anexample embodiment of the present invention.

FIG. 3 shows an example of a transmission frame according to the presentinvention.

FIG. 4 shows a transmission frame having identifiers before theprotocol-related and the central station-related signaling data phases.

FIG. 5 shows a transmission frame having a direct identifier only beforethe protocol-related signaling data phase.

FIG. 6 shows a transmission frame having an identifier immediatelybefore the signaling data phase related to the central station.

DETAILED DESCRIPTION

FIG. 1 shows a communication network for a communication system. Acentral station 1 communicates via a common transmission medium 11having subscribers 21, 22, 23, etc. in the form of terminals, centralstation 1 being responsible for the coordinating function for mediaaccess (Medium Access Control, MAC) to the jointly utilized medium.Central station 1 may be connected to a higher-level network, so thatterminals can connect to one another and to other subscribers in thenetwork. It is, however, also possible that the central station 1 is notconnected to a network, so that the terminals can only communicate withcentral station 1 and with one another. In this case, the traffic alwaysgoes through central station 1 or the direct exchange between terminalsmust be coordinated by central station 1. A jointly utilizedtransmission medium 11 is a wireless channel, for example, but can alsobe a PON (Passive Optical Network) or an HFC (Hybrid Fiber Coax)network.

FIG. 2 shows the structure of a transmission frame for the communicationnetwork illustrated in FIG. 1. Transmission frames 3 are labeled here asMAC frames, contrary to German Patent Application No. 197 26 120 or A.Krämling et al. “Performance Evaluation of MAC Schemes for Wireless ATMSystems with Centralised Control Considering Processing Delays” EPMCC,Bonn, 1997, where they are labeled as signaling periods. At thebeginning of a transmission frame 3, downlink signaling data phase42—BCH (Broadcast Channel)—appears. It is followed by useful signal dataphase 41 for the downlink. It is labeled as DLCH (Downlink Channel) andincludes N useful data time slots for the DL-PDUs (Downlink ProtocolData Units). Similarly, M useful data time slots are provided for theUL-PDUs (Uplink Protocol Data Units) for useful signal data phase 51 ofthe uplink ULCH (Uplink Channel). Uplink signaling data phase 52 islabeled as RACH (Random Access Channel).

Download signaling data phase BCH is divided into two categories asshown in FIG. 2: a signaling data phase 421 related to the centralstation—BCCH (Broadcast Control Channel)—and a protocol-relatedsignaling data phase 422—FCCH (Frame Control Channel). In BCCH 421,central station 1 can forward information to the terminals that is ofglobal relevance for central station 1 and the communication with theconnected terminals. This includes information such as capabilities ofthe central station, manufacturer information, current operating modes,and address of the central station. On the other hand, FCCH 422determines the structure and the contents of the remaining transmissionframe 3 (MAC frame). Thus, FCCH has primarily local, MAC frame-relatedimportance. In FIG. 2, which only shows the principle of the framestructure, BCCH and FCCH are shown directly following one anotherwithout taking into consideration the frame structure according to thepresent invention which is explained below.

Initially we shall assume that the position of the BCCH which containsthe global information is always located at the beginning of MAC frame3. In this case, it is advantageous if the position of FCCH 422 isannounced in BCCH 421. Furthermore, it can be advantageous if a specialidentifier is transmitted immediately before the occurrence of FCCH 422in addition to the identifier at the beginning of MAC frame 3 (see,German Patent Application No. 197 26 120 and Karsten Brüninghaus, MarkusRadimirsch, “Coarse Frame Synchronisation for OFDM-Based WirelessCommunication Systems,” PIMRC, Boston, 1998). It is advantageous if thisidentifier is different from the identifier at the beginning of MACframe 3; however, in principle, it may also be identical to it.

An exemplary MAC frame 3 for a device according to the present inventionis illustrated in FIG. 3. MAC frame 3 begins with an identifier 6, whichunambiguously indicates that this is the beginning of the MAC frame. Anexample of such an identifier is described, for example, in GermanPatent Application No. 197 26 120. It is followed by signaling dataphase 421—BCCH—which contains, among other things, the time interval(indirect identifier) between BCCH and FCCH-T index (BCCH-FCCH). Thisinformation is evaluated by terminals 21, 22, 23, etc., so that FCCH canbe demodulated in a controlled manner as needed.

For this purpose, reference points in time are established; these arethe end of the BCCH and the beginning of the FCCH in the exampleaccording to FIG. 3. The time reference of the BCCH may also be locatedat the beginning or at a point in time in the middle of the BCCH or itmay be the identifier itself. The reference point in time of the FCCHcould also be at the beginning or at some point in the middle of theFCCH. A terminal may also receive this time interval T index (BCCH-FCCH)as a fixed value from the manufacturer. This interval can also bedetermined on the basis of manufacturer-specific considerations or froma standard.

Another option is a flexible interval T index (BCCH-FCCH), which iscalculated by central station 1 as a function of the requirements ofeach situation and communicated to the terminals. The current intervalcan be transmitted to the terminals in the BCCH. This allows the entireDLCH 41 (Downlink Useful Data Signal Phase 41) to be filled if thelength of the DL-PDUs is not constant, as explained previously, but iscomposed of elements having different durations.

The granularity of this time interval can be measured in system cycles;in general, the system clock is specified in a standard. Another optionis the explicit specification of a time granularity which may be theduration of the smallest unit from which a DL-PDU can be composed, forexample. This time granularity is a common divisor of the durations ofall possible DL-PDUs. The function of the FCCH is described in detail inGerman Patent Application No. 197 26 120 and A. Krämling et al.“Performance Evaluation of MAC Schemes for Wireless ATM Systems withCentralised Control Considering Processing Delays” EPMCC, Bonn, 1997; itassigns time slots to the terminals for reception and transmission. Boththe chronological sequence of the individual elements of a MAC frame 3and the effects of the FCCH are specified there. A terminal that wishesto log onto the network can calculate the position in time of theremaining elements of MAC frame 3 and, of course, also of the RACH fromthe information of the FCCH and, using this information, begincommunicating with the central station.

Additional possible embodiments of the present invention are presentedbelow:

BCCH 421 is not located directly at the beginning of MAC frame 3, buthas a constant distance from the beginning of the MAC frame.

It is also possible to identify the position of FCCH 422 through anadditional identifier. In this case, the following combinations arepossible:

an additional identifier 62 is transmitted before FCCH 422; thisidentifier can be advantageously distinguished in the receiver fromidentifier 61 located before BCCH 421. It is also possible that FCCH 422is announced in BCCH 421 or that BCCH 421 announces the position of FCCH422. This is illustrated in FIG. 4.

no identifier is inserted before BCCH 421, so the identifier 62 beforeFCCH 422 is unique and it unambiguously identifies the position of FCCH422. Also in this case, FCCH 422 may or may not be announced in BCCH421. This is illustrated in FIG. 5.

If the position of BCCH 421 is not located at the beginning of MAC frame3, which is provided with identifier 6 as a frame identifier, it may beadvantageous to transmit an easy-to-detect additional identifier 61immediately before BCCH 421. This is illustrated in FIG. 6. Here too, anadditional identifier may be inserted before FCCH 422; identifier 61 maybe present before BCCH 421 or it may be omitted.

1. A method for transmitting data on a common medium in a systemincluding a central station and a plurality of subscribers, data packetsin the system being transmitted from the central station to thesubscribers (downlink) and from the subscribers to the central station(uplink), the central station being responsible for coordinating mediaaccess via a protocol-oriented transmission frame, the transmissionframe including a useful signal data phase and a signaling data phasefor the uplink and the downlink, the method comprising: dividing thesignaling data phase for the downlink into a signaling data phaserelated to the central station and a protocol-related signaling dataphase; providing at least one identifier of a position in time of theprotocol-related signaling data phase of the downlink in thetransmission frame; and including the at least one identifier directlyin the signaling data phase for the downlink.
 2. The method according toclaim 1, further comprising: announcing the position of theprotocol-related signaling data phase, the position being announced inan announcement in the signaling data phase related to the centralstation, the announcement for indirectly identifying theprotocol-related signaling data phase.
 3. The method according to claim1, wherein the announcement contains a time interval of theprotocol-related signaling data phase.
 4. The method according to claim1, further comprising: providing a subscriber-related signaling dataphase at a beginning of the transmission frame.
 5. The method accordingto claim 1, further comprising: providing a first one of the at leastone identifier immediately before the signaling data phase related tothe central station, the first one of the at least one identifier foridentifying a beginning of the transmission frame.
 6. The methodaccording to claim 1, wherein a time interval between the signaling dataphase related to the central station and the protocol-related signalingdata phase is a fixed value.
 7. The method according to claim 1, furthercomprising: communicating to the subscribers via the central station atime interval between the signaling data phase related to the centralstation and the protocol-related data signaling data phase, the timeinterval between the signaling data phase related to the central stationand the protocol-related signaling data phase being variable.
 8. Themethod according to claim 1, wherein a time interval between thesignaling data phase related to the central station and theprotocol-related signaling data phase is filled with useful data.
 9. Themethod according to claim 1, wherein the signaling data phase related tothe central station is at a constant distance from a beginning of thetransmission frame.
 10. The method according to claim 1, furthercomprising: providing reference points in time for the signaling dataphase related to the central station and the protocol-related signalingdata phase, the reference points in time being located one of: i) in abeginning of a respective signaling data phase, ii) in a middle of arespective signaling data phase, and iii) in at least one of the atleast one identifier.
 11. The method according to claim 10, furthercomprising: providing a first one of the at least one identifier beforethe signaling data phase related to the central station and a second oneof the at least one identifier before the protocol-related signalingdata phase, the first one of the identifier and the second one of the atleast one identifier being different from one another.
 12. The methodaccording to claim 11, wherein the first one of the identifier and thesecond one of the identifier being different from one another regardlessof whether a position of the protocol-related signaling data phase isannounced in the signaling data phase related to the central station.13. The method according to claim 1, further comprising: providing theat least one identifier only before the protocol-related signaling dataphase regardless of whether a position of the protocol-related signaldata phase is announced in the signaling data phase related to thecentral station.
 14. The method according to claim 1, furthercomprising: providing an additional identifier of the transmission frameindependently of the at least one identifier.
 15. A method fortransmitting data on a common medium in a system including a centralstation and a plurality of subscribers, data packets in the system beingtransmitted from the central station to the subscribers (downlink) andfrom the subscribers to the central station (uplink), the centralstation being responsible for coordinating media access via aprotocol-oriented transmission frame, the transmission frame including auseful signal data phase and a signaling data phase for the uplink andthe downlink, the method comprising: dividing the signaling data phasefor the downlink into a signaling data phase related to the centralstation and a protocol-related signaling data phase; providing a firstidentifier of a position in time of the protocol-related signaling dataphase of the downlink in the transmission frame; and deriving the firstidentifier of the position in time of the protocol-related signalingdata phase of the downlink from a second identifier, the secondidentifier being provided for a position of the signal data phaserelated to the central station.